Preparations for climate change's influences on cultural heritage Open Access

Significant climate change can be expected globally in the coming years (IPCC, 2007). This has been well known for several years and was in 1998 documented as a problem to be solved by The Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC, 1998). Most, if not all, countries will in the coming years experience the results of the climate change one way or another. Some parts of the world will experience a drier climate, whilst other parts will experience increasing precipitation. An increase of surface water could make flooding and landslides occur with higher frequency in some locations. Increase in sea temperature and melting ice caps and glaciers will lead to sea‐level rise. Furthermore, some regions must anticipate an increase in powerful storms and winds. It is expected that the impact of climate change will vary on local, regional, and national levels. Norway can, for instance, expect more wind and precipitation and higher temperatures, leading to more frequent occurrence of floods, storms, and driving rain (Hanssen‐Bauer et al., 2009).

Some parts of the environment must be considered non‐renewable resources, and thus are irreplaceable. An example is cultural heritage. Cultural heritage includes archaeological remains, cultural environments, infrastructure, buildings, and interiors as well as details and objects. Climate change will probably speed up or change the degradation processes of the cultural heritage. Climate change influences people and the environment, directly and indirectly. A main indirect impact will be policies related to higher energy efficiency in protected buildings. When comparing direct and indirect impacts of climate change on cultural heritage in Norway, the policy changes leading to indirect impacts are likely to be of significant relevance, maybe even of greater relevance, than the direct impacts.

This topic of climate change impacting cultural heritage is of specific concern for owners, authorities, and scientists (Brischke et al., 2010; Cassar, 2005; Gobakken, 2010; Sofronie, 2008; UNESCO, 2009). If a protected building is severely damaged, it will not be possible to get it back in its original form. The building can probably be reconstructed with new materials but the original building will be lost forever, such as trying to reconstruct a centuries old stave church (Plate 1) with modern materials. Heritage sites, like grave mounds and cairns, have the potential for even larger losses. Damage to their contents such as pottery and metal works cannot be repaired by replacing materials.

Many moveable objects are placed in museums or buildings that protect them from many aspects of climate change. The main issue is how to protect in the best way the rest of the cultural heritage which is still exposed. An example is predicting whether flooding will influence a building site and, if so, then how. Furthermore, one must consider the effect that increased rainfall and altered precipitation patterns may have on buildings, sites, and landscapes. Climate change is likely to give more wet‐dry‐cycles and these will accelerate the crystallisation of salts in stone‐ and brick‐constructions. Measures must be implemented to reduce the impact of this and to preserve the remains for future generations. A particularly high risk exists of biological degradation due to wood moisture exposure, especially where there has not earlier been critical moisture stress (Kaslegard, 2010). This is partly because constructive protections no longer function as earlier, so new, complex damage can occur.

In the European project Noah's Ark (2004), climate change effects have been modelled on historic buildings. A building simulation program has been used on models of buildings and made it possible to predict climate change effects regarding, for example, relative humidity due to higher precipitation (Noah's Ark, 2004). A central issue for protecting the cultural heritage from the coming direct impacts of climate change is knowing what to be aware of and how to handle these problems.

It is to a large extent possible for researchers and experts to predict the main threats to cultural heritage. This leads to a responsibility to inform the authorities and owners who are responsible for cultural heritage preservation of these risks.

This problem is international and some projects and collaborations dealing with these problems have started up in other parts of the world. One example is Climate for Culture (2009), funded by the European Commission from 2009 to 2014 and consisting of 30 partners. In the project the damage potential of climate change on cultural heritage will be studied. Both buildings and collections in historic buildings in different parts of Europe are included in the project and climate evolution scenarios will, together with building simulation models, identify the risks related to climate change. Identified risks, together with possible mitigation strategies, will be reported to policy makers. Another example is a Nordic project about the effects of climate change on cultural heritage (Klima og kulturarv, 2009). The main aims of the project are to increase the knowledge of the effects of climate change among people working with cultural heritage and to strengthen the cooperation amongst Nordic countries for this topic.

UNESCO (2008, p. 9) contains, among others, the following principle:

One challenge is to take the step from climate scenarios and adaption strategies to the direct hands‐on maintenance and restoration of old valuable buildings and monuments (Cassar and Pender, 2005).

A practical problem is how to inform the owners and responsible authorities about the normal risk of biodeterioration and other kinds of degradation, and how to identify risks related to climate change. If this can be done, it would enable detection and reaction upon early warning signs of an unusual situation. Information, training and production of both general and specific plans for action in case of change of exposure and extreme situations are of importance in order to prevent the negative effect of climate change (English Heritage, 2008a, b, 2011). In Norway, the Directorate for Civil Protection and Emergency Planning has established a web site which collects important and new information about climate change and how to handle it (Klimatilpasning, 2010). It includes several aspects of the effects of climate change with examples being buildings, nature, health, infrastructure, agriculture, and tourism.

This project has focused on how municipalities in Norway can prepare for and adapt to climate change and extreme weather events. It has been an interdisciplinary project, involving collaboration amongst seven environmental research institutes, where competence on how to prepare for climate change in Norwegian municipalities has been broadened. The project has been carried out by identifying and analysing climate change‐related challenges faced by municipalities. Based on the results, suggestions for mitigation and adaption strategies have been developed.

Several case study municipalities have been used during the work. The mitigation and adaption strategies must be expected to be constantly changing when new research insights are reached. Thus, one of the central issues when trying to disseminate the results has been to provide the municipalities with something more dynamic than static reports or books on the subjects, which could easily become out‐of‐date. This research field is expected to develop in years to come, so printed information could have a rather short life. Instead, web‐based publication was used within this project to be a dynamic information source.

Furthermore, this work focused on the process of detection and monitoring of changes, damage, or deterioration. One of the most important aspects to address is a systematic approach that catches changes at an early stage so that interventions can be conducted.

The main result for the target audience is a methodology dealing with the problem step by step and a product being a web site (Klimakommune, 2010) which can be used as a tool with several possibilities to find practical advice. Examples are how increased precipitation and flooding events can influence cultural heritage, including both monuments and buildings including the interior. Each single monument will be exposed to different threats and will require various measurements, different monitoring, and different treatments.

This paper describes some of the practical threats related to climate change, based on the work done in this project. Suggestions are provided for mitigation and adaption strategies.

Some of the expected consequences of climate change for buildings and infrastructure will occur as events, such as high moisture content due to flooding. Other consequences can be slow degradation of stone materials due to salt crystallisation and biodeterioration of wood due to increased precipitation. Knowledge about the natural degradation processes is necessary as a base for further investigations.

The buildings and infrastructure will probably be threatened mainly by rising moisture content, caused both by direct precipitation and longer periods of high relative humidity. This influence can, for example, give an increase in microbiological decay in the wooden parts of buildings and mould damage on various surfaces. In addition, the higher moisture content can give an increase in salt‐crystallisation in stone constructions. More salts will be transported by water and crystallise in the construction. Regions that until now have had cold and stable winters will in the future experience more frequent fluctuation of the temperature around the freezing point. These fluctuations will result in an increase of freeze/thaw cycles which cause frost damage.

Furthermore, different insect attacks (e.g. house longhorn beetle, common furniture beetle, and carpenter ants) might be more common and extensive due to changes in temperature and humidity. Snow loads on roofs will probably fluctuate more than earlier and from time to time they will be heavier than ever experienced. This threat will actualise the question of reinforcement of the roof constructions of old buildings, especially where the materials already have local constructive or biological damage.

The web site that was developed through this project (Klimakommune, 2010) is designed in a hierarchical way, separating selected thematic topics – drinking water, cultural heritage, and the natural environment focusing on floodplains – at the top and with practical advice in fact sheets within each category. Examples of fact sheets from the cultural heritage theme are “the impact of climatic conditions on biological decay of cultural heritage”, “wood destroying insects”, “mould damage”, “wood‐decaying fungi”, “methods for surveying damage caused by biodeterioration”, “cultural heritage and snow loads”, and “salt crystallisation in stone and mortar”.

All cultural heritage is, to various degrees, naturally exposed to physical, chemical, and biological influences. Which organisms occur in wood and how they tend to grow is knowledge that is relatively well known (Alfredsen et al., 2005). Geographical position plays an important role, where the experience of exposure from local weather conditions gives an important understanding of the general risk of decay (Häglund et al., 2010). In recent years, more focus has also been placed on the importance of the condition of the specific material in situ (Gobakken et al., 2008).

Under normal situations, both exposure and the damage this might cause are, from experience of local conditions, relatively predictable (Figure 1). In case of a change of the exposure, the response can be uncertain. Any damage caused by this changed exposure is more or less unpredictable, due to lack of knowledge and experience (Figure 1). This leads to problems in reacting on early warning signs and performing the proper measurements. Such cases occur, for example, when a building is moved to another area or if the building is modernised or gets new materials. Even the effect of changing the use of the building might be of crucial importance. However, such changes are mostly planned and can be reversed if desired. A bigger problem is climate change, which can be hard to recognise because either the changes occur so slowly that they are not detected in time (e.g. longer periods with rain or higher temperature), or the effect is a side effect of the exposure (e.g. driving rain which causes wet conditions in wooden floor beams inside a brick wall). Only active and in‐depth monitoring and surveying can reveal these problems. The monitoring has to be based on a risk analysis dealing with all aspects of possible damage to the cultural heritage related to climate change. Since possibilities to reduce exposure due to climate change are generally lacking at wider scales, it will often be necessary to improve the climatic shelter of the cultural heritage at smaller site scales.

Several specific examples of the development of damage potentially linked to climate change are now provided.

In most parts of Norway, the climate change models project increased precipitation (Hanssen‐Bauer et al., 2009). In addition, an increasing part of precipitation will come as rain and not as snow. This will give more wet‐dry‐cycles, which means that there will be more cycles yielding wet materials that dry out and then get wet again. In addition, increasing wind will increase driving rain, giving the water more possibilities for penetrating into materials. Since precipitation will increase, soil around cultural heritage will be moister and that level of moistness will remain for longer periods. This will make the lower parts of buildings more threatened by a high moisture content and thereby a higher amount of soluble salts.

As soil moisture increases, increased salt mobilisation leads to more damage on decorated surfaces. The described phenomenon has always existed but will probably increase in the coming years with climate change being an influence. For example, Young et al. (2006, p. 15) write that “Crystallisation and dissolution of salts caused by wetting and drying affecting standing structures, archaeology, wall paintings, frescos and other decorated surfaces” as an example of climate change impacts on cultural heritage. In recent years, computer models have been created of water movement in stone, based on data from previous studies, which can help conservationists and engineers to choose treatment methods over the longer term that take climate change into account (Hall et al., 2010).

All kinds of stone and brick constructions have salts in one amount or another in the materials. The kind of salt is often related to the building materials, and sometimes to the environment such as the groundwater and air pollution. Some common kinds of salts are carbonates (CO₃), sulphates (SO₄), chlorides (Cl₂), and nitrates (NO₃). When water penetrates into an old stone construction made of mortar and brick or stone, such as through driving rain, the water transports the soluble salts. After the rain, and when the water transport has stopped, the constructions will start to dry and the relative humidity in the construction will get lower and lower. Each salt has its defined equivalent relative humidity, RH_eq, which is the upper limit at which it crystallises (Table I).

When it crystallises, it expands (Figure 2), making small cracks in the construction. Since the cracks make air penetration into the construction easier, the relative humidity gets even lower and more salts crystallise.

The crystallisation can give severe damage to old stone or brick buildings. An example is the industrial buildings from the nineteenth century at Kistefos near Hønefoss in the southeast part of Norway (Plate 2). The brickwork has always been naturally exposed to periodically high moisture content during autumns and winters. Heating inside, good maintenance of the buildings, and periods with drier weather outside has made it possible for the brickwork to dry out. Recently, little activity takes place inside the buildings since the industrial period is over, so the buildings are used just as museums. Less heating and less maintenance in combination with higher precipitation in the directions exposed to driving rain makes the risk for salt crystallisation increase.

Counter‐intuitively, damage occurs more easily and creates more problems if the constructions have been repaired with modern materials, such as cement mortar, which are not as open to damp and water intrusion as the old kind of lime mortar. Since cement mortar is more impermeable, the water does not penetrate as easily as in an old construction, but if there is a small crack and the water penetrates, it will create a concentrated salt crystallisation area that can make severe damage to the construction. In addition, some of the modern building materials have salts themselves which will contribute to the risk for salt crystallisation.

Most parts of Norway can probably expect a higher risk of salt crystallisation in the coming century, especially in the coastal regions (Figure 3). In some of these parts, an increase of precipitation of more than 20 per cent is expected (Hanssen‐Bauer et al., 2009) and this will give higher risks for salt crystallisation.

Another example is from the west coast region of Norway were Moster Church is situated. It is a medieval church which over several years has had problems with both biological decay and salt crystallisation. The region has a very wet and windy climate, but heating the church has decreased the biological decay and increased the salt crystallisation. The predicted increase in rain and wind will probably make the problems even worse and the projected climate change in that region makes it urgent to find new solutions.

All kinds of masonry that can be exposed to water will be threatened. Examples are ruins, foundations, and outside walls. To lower the risk for salt crystallisation in a construction, the main action should be to decrease the risk for water to penetrate into the materials. This means that it will be even more important to protect the buildings or ruins from leaks and drainage problems. For example, roofs must be sealed, drain pipes must work well, and the drainage system around buildings and ruins must function. Mountings have to be tight and there should not be any damage to mortar or plaster. The surface treatment on walls, doors, and windows must be in good condition and must be maintained.

To monitor the situation and to prevent damage before it becomes too great, buildings and ruins must be regularly investigated and monitored regarding moisture and humidity. To achieve this monitoring, instruments regularly recording measurements of moisture and humidity are useful as well as frequent photographs. The normal, baseline situation has to be documented, so that a future comparing measurements and pictures can give a good early warning system which is accurate and easy to perform.

Projected climate change might impact biodeterioration in cultural heritage through three main reasons:

• 1.

  higher temperature;

• 2.

  higher relative humidity; and

• 3.

  higher moisture content in wood.

These factors are general effects which individually and combined tend to be favourable for mould fungi, wood‐decaying fungi, and wood‐destroying insects.

In most areas of Norway, climate change is expected to give longer periods with favourable conditions for growth and activity of fungi, insects, and other organisms. This effect will have greatest impact when the temperature rises above 0°C, because this will mean a change from no activity below freezing to various biodeterioration processes above freezing. Cultural heritage in north Europe, and especially in polar areas, will be influenced by this change. However, it is important to remember that these suggestions are quite general based on projections for larger areas. The actual influence has to be examined specifically for every single building, surface, and material.

Biological activity is directly connected to temperature (Figure 4), so an increase of temperature will directly increase the risk of biodeterioration (Mattsson, 2004). On the other hand, temperature changes alone do not necessary automatically have a positive effect on the rate of biodeterioration. Temperature rise alone would give higher activity, but at the same time cause drier conditions in the absence of moisture increases, which might then lead to an overall decrease in biodeterioration risk.

Climate change can, due to increased precipitation, give higher relative humidity and higher moisture content in and around buildings and building materials. This can occur both as a general effect at raised average temperature and due to periods of extreme weather, such as storms, floods, and the combination of rain and wind producing driving rain. Previous examples including the large flood in southern Norway in 1995 and extensive periods of rainfall in southern Norway in the autumns of 2000 and 2005 (Rauken and Kelman, 2010). During these periods, the higher relative humidity caused mould growth on surfaces in constructions that had never been attacked before.

An example of what extraordinary driving rain can lead to is from the medieval church at Talgje in the costal area outside Stavanger in south west Norway. Here, weather exposure has always been of great importance, but due to a robust stone construction, it has never caused any known moisture problems indoors. During a period through one recent winter of more extensive rain and wind than normal, the masonry became soaked. This gave wet conditions on the inside parts of the walls and the interior of the church, which led to mould damage in the church (Plates 3 and 4).

The result of extraordinary humidity from a flood, even though the water never entered the building, is the next example. In a 160‐year‐old wooden building, there had been an attack of dry rot fungus (Serpula lacrymans) in the lower part of the log walls for many years (Plate 5). Owing to relatively dry conditions, the fungus grew slowly in the materials. Then, due to a flood in the neighbouring area, the soil, floor construction, and the lower part of the walls became exposed to moisture from the ground. This gave the already established fungus excellent growth conditions which led to extensive damage in three months (Plate 6) even though the building itself was not flooded.

Field studies at Svalbard (Spitsbergen) have shown how the rate of biodeterioration in building materials is influenced by thawing of the permafrost (Mattsson and Flyen, 2008). Traditional practices of soil up against walls ensured good protection against wind, cold temperatures, and surface water. At the old trappers hut on the west coast of Svalbard, the soil had been against the wall for 90 years (Plate 7). During recent years, the permafrost has disappeared during summertime due to temperature increases, so the frozen soil has thawed. The result was an intrusion of water through the lower parts of walls and the wetting of the inside of the building (Plate 8). This caused new damage from both mould and wood‐decaying fungi.

In order to be able to know if any changes are happening, the normal situation has to be documented. This can be done by traditional building surveys, where knowledge of different kinds of organisms and damage is recognised. As an aid to identifying the problems, fact sheet where various aspects of biodeterioration are described have been developed (Klimakommune, 2010).

With such basic information of the situation for the cultural objects, it is possible to predict the future rate of biodeterioration. Based on this knowledge, action plans can be developed, for different possible problems. By monitoring critical aspects, any deviation from the expected normal or baseline can be detected at an early stage. Suitable remedial actions can then be started in order to reduce the negative consequences. Over the long term, many effects of climate change probably could be handled reasonably well by changing maintenance. Exceptions might be damage caused by sea‐level rise, landslides, and other major changes in the landscape.

Improved knowledge of possible local changes of exposure, both caused by humans and the more natural exposure regime, will give better possibilities to observe and react regarding early warning signs of abnormal exposure. The improved knowledge can be based on surveys of damage including, for example, sampling, analysis, and monitoring. This will ensure the possibility for reacting before damage is too far developed, regardless of whether the actions need to be traditional or new, remedial or preventive (Figure 5).

Change in climate occurs continuously and it is, and always has been, a normal process. However, when the changes come rapidly and have a direct influence on the decay of cultural heritage, it is advisable to react in order to preserve the materials as much as possible in the new situation. The main threats, how to deal with them, and the most important advice are summarised as follows:

• Microbiological decay in wooden constructions will probably be one of the greatest problems related to climate change in Norway, and around the Nordic region, and has to be continuously monitored.

• Information and training have to be given to cultural heritage owners and authorities in order to limit the negative effects of climate change that might occur in the future.

• Routines and methods for surveys have to be established in order to be able to reveal and react to unusual exposure situations.

• Ordinary maintenance is of crucial importance in order to handle normal exposure. This also gives a possible buffer effect for extreme situations.

• Repairing buildings and constructions must be kept up and intensified, especially regarding the influence of higher humidity and higher moisture content due to higher precipitation and wind load as well as snow load.

As well, the focus on this paper has been mainly direct effects. The realm of indirect effects requires further exploration to ensure that the initial analysis, suggesting that indirect effects were of less consequence for cultural heritage, was indeed correct. Climate change has many possible effects, so it is important to ensure that they are all considered for the preservation and maintenance of heritage.

Annika Haugen is a Research Scientist/Graduate Engineer in the Building Department of the Norwegian Institute for Cultural Heritage Research (NIKU). Her main areas of interest are climate adaptation in older buildings and technical subjects regarding brick and masonry constructions. Annika Haugen is the corresponding author and can be contacted at: annika.haugen@niku.no

Johan Mattsson is the Leader of Research and Development at Mycoteam A/S in Oslo, Norway. His main areas of interest are biodeterioration of cultural heritage in Norway and the polar regions, indoor air quality, and mould decaying fungi and wood‐boring insects.